Felted fibrous composition



5 commercially practicable.

Pangaea Sept. 20, 1932 UNITED STATES.

PATENT OFFICE EARL r. srnvnnson, or nnwron, AND HARRY A.

BURON, OF. CAMBRIDGE, MASSACHU- SETTS, ASS IGNORS TO THE RICHARDSON COMPANY, OF LOCKLA'ND, OHIO, A CORPO- RATION OF OHIO No Drawing.

Our invention is related' to the formation of special types of feltable pulps in which bitumen or other heat plastic material in minute, uncoated particles exists in stable association with fibrous material in water suspension. In our co-pending application, Serial No. 316,611, filed November 1, 1928, we have set forth and claimed a general method of making pulps containing bitumen 1) and other heat plastic material. Our pres ent invention has to do specifically with the solution of special problems in connection with the use of asbestos as a fiber in said pulps, and one of its objects is to facilitate the use of asbestos therein. In like manner the present invention facilitates the.practical manufacture of other paper or felt mill products in which it is desirable to include a substantial percentage of long fibered stock. A bituminous fiber base for roofing and fioor coverings falls into thiscategory.

Another of our objects is to provide a bituminous pulp containing asbestos having a greater fiber length than has hitherto been Other objects of our invention are the formation of felted sheets or boards containing asbestos and bitumen or other heat plastic material which may be considerably modified to meet "vary- 3 ing commercial uses.

These and other objects of our invention which will be pointed out hereinafter, or will be apparent to one skilled in the art upon reading these specifications, we accomplish by that certain process, and in that product, of which we shall now describe a preferred embodiment.

In the formation of bituminous pulps in accordance with the co-pending application hereinabove referred to, an exemplary practice comprises introducing wetted fibrous material into a mixing device exemplified by the well-known Werner-Pflciderer type, and there mixing it with bituminous material, such as. asphalt softened by heat, but without driving out all of the water in the fibrous material. When the mixing has been continued so as to bring about a preliminary association between the fibrous material and bituminous material (generally to the point rELrEn rumou s oorrrosrrion Application filed July 14, 1930. Serial No. 467,964;

of visual homogeneity), more water is added to the mixture, whereupon the pulp breaks down and comes into a loose mass which canbe transferred to a paper mill beater or the like, and beaten into a feltable stock. This stock or pulp, although it may contain widely varying and very large percentages of bitumen, is a true pulp and may be handled as any other paper pulp, and felted out upon a screen into a sheet.

When the same procedure is adopted with a mineral fiber, such as asbestos, a certain difficulty arises in theretension of roper fiber lengths, because the mineral ii brittle, and both the mixing, which is the pre-association stage, and the beating, which is the pulping stage, are mechanical operations tending to shorten the fibers.

Broadly, our invention comprises the introduction of the fibrous ingredient in two stages in the formation of a bituminous pulp, in one aspect; and in another. aspect it comprises the use of two different characters of asbestos or other mineral fiber with resultant economy; In following out our invention we use, preferably, a short fibered asbestos in the mixing or pre-association stage, and having first produced a mixed mass of this fiber and a bitumen or other heat plastic material, and having broken it down as hereinabove described, we transfer it to a beating engine, and'during the pulping thereof, we add a longer asbestos fiber in the quantity necessary to bringthe fibrous content of the finished pulp to the desired value.

In an exemplary process we may introduce into a mixer, say, 75 parts by Weight of short fibrous asbestos, which may contain substantially no fiber longer than 2-3 millimeters. To this we may add 150 parts of an asphalt having the following characteristics:

Ball and ring softening point 142 F.

Penetration range of Grams Seconds 108 at 115 ..v

ber isthe mixing operation the temperature of the with vegetable fibers, because asbestos fibers are non-absorbent. At the end of the mixing operation the mass may be transferred directly to a beater; but we preferto 'add more watef first to the mixer and continue the revolution of the blades until the mass has broken down and comes nto a condition which is easily handled by the heaters. l/Ve then transfer the material to a Hollander or other beating engine and pulp it as is usual in other paper makingoperations. During the pulping stage we may add a longer fibered asbestos material that is of a length averaging above fivemillimeters. The beating is continued with such dilution as may be required, until the pulp isin condition for felting upon a screen. Further refining may be practiced if necessary. a

The felting of this pulp into sheet form may be accomplished on an ordinary wet machine commonly used for making board. The felted sheet can then be dried under the proper conditionsof heat and pressure required to develop the properties of the binder used.

We havev found that by this procedure we can make a felted product containing bitumen or other heat plastic in varying proportions up to 75% of the total solids, and asbestos in which the fiber length is substantially retained.

Masses of wetted asbestos fiber and asphalt or other heat plastic binder do not absorb water at the dilution or break-up stage of the process as readily as in the case of vegetable fibers. Depending upon the kind of binder and the ratio of binder to fiber it .may be necessary in some cases to use a small percentage of a vegetable paper making fiber, for example, old news in admixture with the short length asbestos. Generally it will be found suflicient to use an amount of new stock corresponding to 1020% of the total fiber content of any given composition. This assisting fiber should all be added at the mixing stage.

It will be understood that the ingredients and proportions in the above formula are exemplary only, and are not limiting. Our invention is capable of wide modifications as to proportions and materials. Itis not necessary to start with short-fibered asbestos in the pro-association stage, but it is commercially advisable to do so because of the shortening action on the fibers. With the introduction of all of the fibrous material into the mass in pro-association stage, we have not been able to retain any great fiber length in the final product; but by the process hereinabove described we have found it possible to add a substantial percentage of long fibered asbestos and to retain its fiber length substantially unimpaired in-the finished prod uct. e have further found it advantageous from the product point of view, to have both a percentage of long fibered asbestos and a percentage of short fibered asbestos in the finished product.

lVe are not restricted in the broad aspects of our invention to the use of asbestos or other mineral fibers alone. We may, for example, form a massto be pulped by a preassociation step carried on with bitumen and vegetable fibers alone or in admixture with short length asbestos, and then add long fibered asbestos during the pulping stage. The character of the fibrous material and the character and relative quantity of the bituminous material will be varied in accordance with the kind of product desired, as will readily be understood. By this process not only bitumen, but in like manner, other binders, such as gums, natural resins, pitches, drying oils, rubber compositions and synthetic resins, etc. can be incorporated with asbestos fiber.

The foregoing procedure is particularly well adapted to the manufacture of a Wide variety of paper or felt mill products in which existing standards require a substantial percentage of long fibers in the finished product. In such classification fall sheeted asbestos composition and saturated rag felt for use in roofing or felt base floor coverings. In the latter case it may be found advantageous to add all of the long fibered rag stock to the beater and to carry on the asphalt or bitumen Among the products which can be advan tageously manufactured by the foregoing procedure is a new and improved type of electrical insulation containing substantially only asbestos fiber and a di-electric binder .of which bitumen or asphalt is an example. As a substitute for the usual asphalt saturated paper or felt, such an asbestos product possesses the advantage of-immunity to climatic changes, such as humidity. This product can be most advantageously formed on a wet lap machine and built up thereon from relatively thin laps followings in general the well-known procedure for the manufacture. of press board.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent, is:

1. That process of producing a feltable fibrous pulp containing a heat plastic which comprises first mixing wetted fibrous ma- That process of producing a feltable pulp containing a heat lastic, which comprises pre-ass'ociating a eat plastic and fibrous material of short fiber length, in the presence of water, then pulping the mass so formed, and during the pulping operation adding thereto a quantity of fibrous material of longer fiber length.

3. That process of producing a feltable bituminous pulp which comprises pre-associating a bituminous material and a wet short-fibered asbestos material, pulping the mass'so formed, and during the pulping operation adding thereto a uantity of asbestos fiber of longer fiber length 4. That process of producing a feltable bituminous pulp which comprises pre-associating a bituminous material and a wet short fibered asbestos material, pulping the mass so formed, and during the pulping operation adding thereto a quantity of asbestos fiber of longer fiber length, afterward felting the pulp so formed upon a screen and drying the resultant sheet under heat sufficient to melt the bituminous material.

5. That process of producing a feltable bituminous pulp which comprises pre-associating a wet fibrous material and a bitumen, pulping the mass so formed, and during the pulping operation adding thereto a quantity of asbestos fiber.

6. That process of producing a feltable bituminous pulp which comprises mixing wetted asbestos fiber of short fiber length with bituminous material under heat sufiicient to render it non-solid while maintaining a quantity of moisture in the mass, adding water, and breakin the. mass down to a seml-suspenslon, trans errmg the sem -suspension to a beating engine, and pulping it in the presence of water and during the said pulping operation adding thereto a quantity of long fibered asbestos material. I

7. A process for preparing a fibrous pulp containing asphalt, comprising the steps of reducing asphalt to a viscous condition and adding thereto a predetermined weight ofwet paper, mixing said materials in the -preferred type of mixer as described until a substantially homogeneous condition is in action, an additional amount of. water suflicient to partially break up the adhesive mass of fibers and asphalt, then completing the pulping operation with further addition of water in a beating engine, and finally addin to'the beater a quantity of long fibered as estos of paper-making grade.

9. That process of preparing a bituminous fibrous combination, comprising the ste of mechanically distributing said bitumlnous material when a non-solid throughout a mass of wetted fibers without the use of an emulsifying agent, the water present being insufiicient to act as a circulating medium, diluting the mixture with the addition thereto of a quantity of fibrous material of comparatively longer fiber length than wood pulp, and thereafter forming a web therefrom on a paper machine.

10. That process of preparing a bituminous fibrous combination, comprising the steps of mechanically distributing said hituminous material when a non-solid through- P out a mass of wetted fibers without the use of an emulsifying agent, the water present being insufiicient to act as a circulating medium, diluting the mixture while adding thereto a quantity oflong-fibered asbestos stock of paper-making grade.

11. A felted paper mill product, comprising asbestos fibers and a heat plastic binder characterized by a binder content in excess of twice the fiber content by weight.

12. A felted paper mill product comprising asbestos fibers and a bitumen characterized by a bitumen content in excess of twice the fiber content by weight.

13. An electrical insulator built up from laps of asbestos fiber stock containing a dielectric heat plastic binder, and further characterized by a binder content in excess of the fiber. I

14. An electrical insulator built up from laps of asbestos fiber stock containing a bitumen, and further characterized by a bitumen content in excess of the fiber.

. EARL P. STEVENSON.

HARRY A. BURON.

reached, thereafter adding to the mixer while in action, an additional amount of water sufficient to partially break up the adhesive mass of fi ers and asphalt, then completing the pulping operation with further addition of water in a beating engine, and

finally adding tothe beater an amount of comparatively long fibered stock.

8. A process for preparing a fibrous pulp containing asphalt, comprising the steps of reducing asphalt to a viscous condition and adding thereto a predetermined weight of wet paper, mixing said materials in the referred t pe of mixer as described until a substantlally homo eneous condition is reached, thereafter a ding to the mixer while 

